I use natural bristle brushes.
My wife usta use foam but she gave it up.
Iíll check at home to see what Rebecca Whitman says about this.

Foam works, but if you use the box store brand, not JENN, your results will be poor. Use a wide mouth container, DONíT scrape the brush against the lip to remove excess, just press it gently against the side. With foam, donít ďbrushĒ, just stroke. Get as much material on as quickly as you can and then let the varnish do its thing. The more you monkey with it, the worse itíll look. Thatís the hardest part of the process! Let it alone!! Long, quick, even strokes. Once you lose the wet edge, youíre done. Go back over it & youíll for sure have a hot mess. Thin the varnish, you may need to thin as you work it. Your job is to get the varnish onto the work as evenly and quickly as you are able, the varnish does the rest!! Donít apply when the sun is on the work or the wind is blowing. Early morning as soon as the dew is off. The slower the solvents flash off, the longer the varnish has to self level, and THAT is what makes the shine! Cool, still mornings are the stuff of which varnish dreams are made!

Foam works, but if you use the box store brand, not JENN, your results will be poor. Use a wide mouth container, DONíT scrape the brush against the lip to remove excess, just press it gently against the side. With foam, donít ďbrushĒ, just stroke. Get as much material on as quickly as you can and then let the varnish do its thing. The more you monkey with it, the worse itíll look. Thatís the hardest part of the process! Let it alone!! Long, quick, even strokes. Once you lose the wet edge, youíre done. Go back over it & youíll for sure have a hot mess. Thin the varnish, you may need to thin as you work it. Your job is to get the varnish onto the work as evenly and quickly as you are able, the varnish does the rest!! Donít apply when the sun is on the work or the wind is blowing. Early morning as soon as the dew is off. The slower the solvents flash off, the longer the varnish has to self level, and THAT is what makes the shine! Cool, still mornings are the stuff of which varnish dreams are made!

I use a good quality bristle brush for varnish. Foam is ok on flat areas but difficult to use on details like corners.

For the final coat on interior varnish, after several coats of varnish, sanding and cleaning, I wipe the varnish on with cloth. The varnish is thinned 10 to 20 percent. I dip the cloth in the thinned varnish, squeeze out most of the varnish and wipe the it on in one direction. No brush marks.

(Apologies for the hijack, but.......) Since we're diving heavy into technique. I'm working on two projects and have not worked with varnish before. With finishes like polyurethane you can finish with fine steel wool to get any imperfections and get a smooth finish.

That doesn't appear to be the case with varnish. I hit it with a fine steel wool and lost the shine immediately.

how do you get the imperfections out and get it smooth to the touch after the final coat?

Terry, I feel your pain brother!!! I have used them ALL. Hair brush seem to work the best. I have only one cap rail and it is around the cockpit. It was the nightmare from hell. Finally after 10 coats it came out shiny....Then I applied only one more and left it alone as I didn't want to screw it up. All I have to say is good luck..

My old friend was a cabinet maker. He did not own a brush. He would take a piece of wool sock the size of a golf ball and place it inside a thin nylon sock. He would hold it in his fingers with the ball in front. The wool would store the varnish and the nylon would apply it without and lint

how do you get the imperfections out and get it smooth to the touch after the final coat?

Ha! You don't!! Therein lies the rub. That's why it's called the final coat. What you get is final. There is no after the final coat, there's only another coat. If you're unhappy with the results of the final coat, that coat just became the next to last coat.
If you're looking for smooth to the touch, you may want to wet sand between coats, I use 400 grit, wet sand VERY early in the morning so you're coating before the sun gets high enough to heat the surface. Add a bit of Dawn to the water to lubricate and add a bit of degreasing quality, then clean with a wet cloth, rinse cloth, clean again, then wipe down with a clean lint free rag and denatured alcohol. Tack off a section just before coating. I cover anything that is in the sunlight until just before I tack it to keep it cool. If it gets warm, the varnish will start to flash off before it floats out...= brush marks. The varnish must have a chance to self-level. As much material as you can get on as quickly as possible and LET IT ALONE. If you are brushing to smooth out the coat, you're just chasing your tail. The varnish will smooth out the coat all by itself! Your job is to provide the optimum conditions for that to occur.

Bugs- are karma coming back to punish you for the time you were cross with your dog.
BTW, the pics are almost last coat... 2 coats CPES, 15 coats Epifanes gloss, wet sanded between coats.